This invention relates to a plasticizing and injecting unit for use in an injection molding machine, comprising a carrier and supply block, a plasticizing cylinder detachably mounted in said block, two hydraulic advance-retract cylinders, which are disposed in said block in bores which are symmetrical with respect to the injection axis and are operable to axially displace the plasticizing and injecting unit along guide rods and comprise pistons which are fixedly carried by said guide rods, and at last one hydraulic injection cylinder for axially displacing a feed screw, which is rotatably mounted in the plasticizing cylinder.